How people work ... and the fingerprint mystery

Why do we chew our food? Research has shown that it is not, as has
long been presumed, to make chunks of food small enough to swallow
without choking. Biomechanics, who have modelled the cohesive strength
of food after a certain amount of chewing, have shown that we actually
chew our food to ensure it is in a firm blob and, therefore, safe to
swallow.

Writing in January's Physics World, Dr Roland
Ennos, a biomechanic in the Faculty of Life Sciences at University of
Manchester, explains how we need to look beyond obvious answers if we
are to understand how our own bodies work.

Explaining why we
swing our arms, why we have notched teeth, why our fingernails always
break in the same direction, and, still puzzling, why we have
fingerprints, Dr Ennos shows how rich the boundary between biology and
physics is in, some counter-intuitive but, potentially significant
discoveries.

On the fingerprint puzzle, we know that
fingerprints are useful to identify people for security and crime
detection, but no scientist has ever suggested that fingerprints
evolved specifically for this purpose. It has been thought that
fingerprints help us to grip more tightly to objects, but tests show
that a rough surface does not actually increase the friction of soft
materials such as skin.

Fingerprint friction is therefore a
mystery that has left Dr Ennos's team testing a number of options - it
could be that fingerprints act like the treads on tyres, removing water
and so increasing friction under wet conditions. Another possibility is
that prints also make the skin more flexible and stop it blistering.

As
Dr Ennos writes, "The answers to these questions may appear obvious or
even trivial, but further thought and experiment is revealing that our
world is far more fascinating than we could have dreamed."

What's
more, this sort of research, unlike many areas of physics, is not
expensive or mathematically hard. "All you need is an enquiring mind, a
bit of ingenuity and the courage to ask awkward questions," concludes
Dr Ennos.